<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<style>
    h1{
        background-color: red;

        width: 500px;
        height: 200px;
        color: black;
        text-align: center;
        line-height: 200px;
        margin: 0 auto;
        border-radius: 25px;
    }
</style>
<body>
<h1>不要想着做坏事好不好哇！警报</h1>
</body>
</html>